ACORN: Measuring the electron-antineutrino correlation in neutron beta decay

F E Wietfeldt ,A Komives,G Darius,B Collett,M S Dewey ,G L Jones ,W A Byron ,M P Mendenhall ,J S Nico ,C Deangelis ,Md T Hassan ,E J Stephenson

doi:10.1051/epjconf/201921904008

Abstract

The aCORN experiment uses a novel asymmetry method to measure the electron-antineutrino correlation (a-coefficient) in free neutron decay that does not require precision proton spectroscopy. aCORN completed two physics runs at the NIST Center for Neutron Research. The first run on the NG-6 beam line obtained the result a = 0.1090 +/- 0.0030 (stat) +/- 0.0028 (sys), the most precise to date. The second run on the new NG-C high flux beam line promises an improvement in precision to ¡ 2%. In addition we show that an improved measurement of the neutrino asymmetry (B-coefficient) can be made using the aCORN apparatus on a highly polarized neutron beam.

Highlights

The most important experimental observables of neutron beta decay are described by the formula of Jackson, Treiman, and Wyld [1]
It is assumed here that the neutrons are in a spin polarization state P, while the beta electron and antineutrino spins are averaged over
Previous neutron a-coefficient experiments measured the shape of the recoil proton energy spectrum and were systematically limited at about 5% relative uncertainty [4,5,6]. aCORN employs a novel “wishbone asymmetry” method first proposed by Yerozolimsky and Mostovoy [7,8,9,10]

Summary

Introduction

The most important experimental observables of neutron beta decay are described by the formula of Jackson, Treiman, and Wyld [1]. Ee, pe, me are the beta electron total energy, momentum, and mass; pν, Eν are the antineutrino momentum and energy; and F(Ee) is the beta energy spectrum. The neutron decay lifetime is τn and the parameters a, A, B, and D are correlation coefficients that are experimentally measured. It is assumed here that the neutrons are in a spin polarization state P, while the beta electron and antineutrino spins are averaged over. In the Standard Model, the neutron a coefficient is given by [1]

The aCORN experiment

Data analysis and results

Systematic effects

Findings

The NG-C run